This application is a 371 of PCT/US99/07608, filed Apr. 7, 1999.
The present invention relates to a multi-layered part and a method of producing a multi-layered part having relatively rigid upper and lower layers, and a viscoelastic intermediate layer. In a particular embodiment, it relates to a method and apparatus for stamping a flat, uniformly edged part from a multi-layered strip, including a viscoelastic intermediate layer, on a mass production basis.
Several well-known techniques are normally employed for stamping or blanking parts from sheets or strips of material. Typically, the part is sheared or cut from the strip by subjecting the strip to shear stresses at desired locations. One common blanking device includes a punch and die or similar punch press tools. The punch and die is shaped in accordance with a desired shape of the end part, and may therefore assume a number of different shapes, including circular, rectangular, etc. Generally speaking, the material strip is placed between the punch and die, and the punch is driven toward the die. During this operation, the part is sheared from the strip along fracture lines imparted by the punch and the die. Other similar shearing techniques including die cutting, fine blanking, steel rules, etc.
While blanking operations via a conventional punch press or similar technique are widely accepted, inherent limitations of these shearing techniques normally impart certain imperfections into the resulting part. For example, with the standard punch/die approach, clearance between the punch and die is a major factor in determining the shape and quality of the sheared edge of the part. During the shearing process, actual shearing normally initiates with the formation of fractures or cracks at the interface areas between the part and the punch and the part and the die. These fractures define deformation zones and eventually meet, resulting in complete separation. With this in mind, the sheared edge of the part is typically neither smooth nor perpendicular to a plane of the strip. More particularly, as clearance increases, the edge of the part becomes rougher as the zone of deformation along the part edge becomes larger. Material is pulled into the clearance area, and the edge of the sheared part becomes more and more rounded. Additionally, burrs are normally formed at the bottom surface of the part. It may be possible to better control fracture formation by incorporating a cutting edge into the punch. However, even with relatively thin strip material, uncontrolled fractures along the sheared edge of the part will still result.
Depending upon the end application for the part, the above-described defects may be of little concern. For example, stainless steel washers are typically produced via a punching operation. For most applications, it is not necessary that the washer be extremely flat or have uniform inner and outer perimeter edges. Further, where flatness and edge uniformity is of greater importance, certain additional process controls can be implemented. For example, a fine blanking operation can be employed in which a V-shaped stinger, or impingement ring, locks the material sheet or strip tightly in place so as to minimize burr formation and facilitate a more uniform shear. Alternatively, additional manufacturing steps, such as rolling, flat baking, shaving, deburring, etc. may be employed.
One particular product normally produced using a punching operation is the disk substrate material for a rotatable storage article such as a computer hard disk. Disk substrates used in computer hard disk drives are typically mass produced by blanking a properly shaped part from a sheet of aluminum. Other materials are subsequently applied to opposing surfaces of the disk, such as plated nickel and sputtered magnetic material. However, the disk substrate itself is produced by a punch and die device. It is estimated that over one billion computer hard disks are produced annually. Obviously, it is imperative that the disk substrate be flat. In this regard, current industry standards require a flatness of less than 8 microns per 96 mm (one typical hard disk substrate diameter) or 5 microns per 84 mm (another typical disk diameter). To satisfy this rigorous standard, a stinger technique is normally employed to minimize burr formation. Further, following the blanking or stamping operation, the disk substrate is typically flat baked.
The above-described techniques achieve the requisite disk substrate flatness due to the monolithic nature of the sheet material. The monolithic aluminum material facilitates successful flat baking because the imperfections imparted during stamping are relatively uniform across the disk thickness. For most end applications, a monolithic or single layered aluminum disk substrate is more than satisfactory. However, as computer hard drive technology continues to evolve, the computer hard disk is subjected to increasing demands. For example, efforts have been made to increase the rotational speed of the hard disk. Hard drives normally spin at one constant speed. Typical speeds range from 3600 to 7200 revolutions per minute (rpm). With recent improvements to hard drive designs, rotational speeds well in excess of 10,000 rpm are available. At these rotational speeds, the disk will begin to flutter or vibrate in response to air drag and/or internal hard drive harmonics. The effects of harmonic motion are greatly increased at higher rotation speeds. Because the standard computer hard disk substrate is monolithic, any resonant vibration generated at a bottom surface of the disk substrate is transferred to, or propagates to, the upper surface (and vice-versa), potentially leading to reading/writing errors.
To overcome resonant vibrational issues, recent disk substrate designs have focused on providing an internal damping mechanism. This internal damping mechanism serves to absorb or damp resonant vibrations, thereby preventing vibration propagation and resulting reading/writing errors. One such computer hard disk substrate (or similar rotatable storage article) is described in U.S. Pat. No. 5,538,774 assigned to Minnesota Mining and Manufacturing Company of St. Paul, Minn. The described disk substrate includes at least one layer comprised of a viscoelastic material. The viscoelastic layer serves to damp resonant vibrations generated during use.
Incorporating a viscoelastic material within a computer hard disk substrate is a highly viable solution to the resonant vibration issue. However, certain manufacturing concerns may arise during mass production. One technique for producing a multi-layered disk substrate, or any other product incorporating relatively rigid outer layers and a viscoelastic intermediate layer, is to prepare each of the three or more layers independently. Once cut to a proper shape and size, the three or more layers are adhered to one another. In terms of mass production, this technique may be relatively time consuming. Further, difficulties may be encountered in properly aligning the layers. Conversely, the three or more layers may be formed into a continuous strip. An individual computer hard disk substrate or other component is then stamped from the strip in accordance with previously described stamping procedures. With conventional stamping techniques, the upper rigid layer effectively cuts at least a portion of the lower rigid layer. Unlike a monolithic part, however, it is exceedingly difficult to xe2x80x9ccorrectxe2x80x9d stamping-caused defects in a multi-layered part incorporating a viscoelastic intermediate layer. Because the viscoelastic intermediate layer is soft and deformable, the rigid outer layer material will easily deform at the interface area with the viscoelastic material. This internal deformation or deflection is more prevalent along perimeter edges of the part. Because the viscoelastic interface area is internally located, it appears to be extremely difficult to correct edge deflections via an external compressive force and/or flat baking. Thus, it may be difficult to meet flatness specifications of less than 8 microns per 96 mm on a mass production basis. Effectively, conventional stamping techniques result in an uneven sheared edge surface and unacceptable flatness deviations. Notably, these same problems will be evident not only in computer hard disk substrates, but also with any other multi-layered stamped part.
Implementation of a viscoelastic material layer between relatively rigid material layers presents substantial improvements to many currently-available products. However, manufacture of these products with known stamping techniques may cause unacceptable flatness deviations. Therefore, a substantial need exists for a method of stamping a uniform, flat part from a multi-layered strip.
One aspect of the present invention relates to a method of stamping a part from an elongated strip of multi-layered material, the multi-layered material including an upper layer, an intermediate layer and a lower layer. The intermediate layer is viscoelastic. The upper and lower layers are relatively rigid with respect to the intermediate layer. The method includes providing a stamping device having symmetrically aligned top and bottom punches. Each of the top and bottom punches includes a material displacement edge corresponding with a desired shape of the part. To this end, each of the material displacement edges are defined by a rake surface and a part interface surface. The rake surface and the part edge interface surface combine to form a positive rake angle. The strip is positioned between the top punch and the bottom punch such that the material displacement edge of the top punch is adjacent the upper layer, and the material displacement edge of the bottom punch is adjacent the lower layer. Portions of the upper and lower layers are then sheared by the top punch and the bottom punch, respectively. More particularly, the material displacement edge of the top punch passes through a portion of the upper layer to form an upper layer groove pattern. Similarly, the material displacement edge of the bottom punch passes through a portion of the lower layer to form a lower layer groove pattern. Each of the upper and lower layer groove patterns define a perimeter of the part. Finally, the part is separated from the strip. The so-produced part has a substantially uniform perimeter edge and is substantially flat.
Another aspect of the present invention relates to a method of stamping a part from elongated strip of multi-layered material. The multi-layered includes an upper layer, an intermediate layer and a lower layer. The intermediate layer is viscoelastic. The upper and the lower layer are relatively rigid with respect to the intermediate layer. The method includes forming a first groove in the upper layer, the first groove defining a perimeter of the part and having a depth less than a thickness of the upper layer. A second groove is formed in the lower layer. The second groove is symmetrical to the first groove and has a depth less than a thickness of the lower layer. In this regard, the first groove and the second groove are formed substantially simultaneously. Finally, the part is separated from the strip. The so-produced part has a substantially uniform perimeter edge and is substantially flat.
Yet another aspect of the present invention relates to a device for partially stamping a part from an elongated strip of multi-layered material. The multi-layered material includes an upper layer, an intermediate layer and a lower layer. The intermediate layer is viscoelastic. The upper layer and the lower layer are relatively rigid with respect to the intermediate layer. The device comprises a first punch, a second punch, a driving mechanism and a stop. The first punch includes a material displacement edge corresponding with a desired shape of the part. Further, the material displacement edge is defined by a rake surface and a part interface surface. The rake surface and the part interface surface combine to form a positive rake angle. The second punch includes a material displacement edge substantially identical to the material displacement edge of the first punch. The first punch and the second punch are arranged vertically such that the material displacement edges are symmetrically aligned. The driving mechanism is configured to force the first punch toward the second punch during a stamping operation. Finally, the stop is configured to control spacing between the material displacement edges during a stamping operation. More particularly, the stop controls the stamping operation such that a vertical spacing between the material displacement edges is preferably greater than a thickness of the intermediate layer.
Yet another aspect of the present invention relates to a part produced by any of the above-described inventions. In one preferred embodiment, the part is a rotatable storage article such as a computer hard disk substrate. Another related aspect of the present invention provides a disk substrate for use as a base component of a rotatable storage article. The disk substrate is defined by an outer perimeter edge and an inner perimeter edge. The disk includes an upper layer, a lower layer and an intermediate layer. The intermediate layer is disposed between the upper layer and the lower layer, and is viscoelastic. The upper and lower layers are relatively rigid with respect to the intermediate layer. Further, the upper layer, the lower layer and the intermediate layer are configured to be substantially planar and substantially parallel to one another from the outer perimeter edge to the inner perimeter edge.